Antireflective coating layers are used, for example, on display screens of display devices, on cover plates of solar collectors, on envelopes of light sources and on other optical elements such as lenses and windows, to reduce reflection losses of traversing light and to suppress disturbing reflections in images.
In U.S. Pat. No. 4,830,879 a method of manufacturing an antireflective layer is described. By means of a reaction of an alkoxide starting material with water various solutions with gel particles are manufactured, which solutions exhibit a graded particle size. Successive layers of solutions having an increasing particle size are applied to a substrate and dried. The layer thus manufactured is porous and exhibits an increasing grain size and pore size in the direction from the substrate surface to the outside surface of the layer. As a result of the decreasing average density in the layer, there is a corresponding decrease of the refractive index. Alkoxides, for example methoxy and ethoxy compounds of silicon, titanium and aluminium are used as the starting material, the optical properties of the layer being adaptable by means of dopants.
A disadvantage of the known antireflective layer is that it is porous and, hence, mechanically weak. This disadvantage also occurs with other methods of rendering substrate surfaces antireflective, for example when the substrate is roughened by means of etching. A further disadvantage of the known method consists in the necessity to use a number of different solutions which are successively applied to the surface and which each require a drying step. Such a method comprises many steps and is unsuitable to be carried out as a continuous method.